The present invention relates to an athletic shoe midsole design and construction. More particularly, the invention relates to a midsole assembly comprising a midsole formed of soft elastic material and a corrugated sheet disposed in the midsole.
The sole of an athletic shoe used in various sports is generally comprised of a midsole and an outsole. The midsole is typically formed of soft elastic material in order to ensure adequate cushioning properties. The outsole is fitted under the midsole and directly contacts with the ground.
Running stability as well as adequate cushioning properties are required in athletic shoes. Consequently, there is a need to prevent shoes from being deformed excessively in the lateral or transverse direction when contacting with the ground.
As shown in Japanese Utility Model Examined Publication No. 61-6804, the assignee of the present U.S. application proposes a midsole assembly having a corrugated sheet therein, which can prevent such an excessive lateral deformation of shoes.
The midsole assembly shown in the above publication incorporates a corrugated sheet in the heel portion of a midsole, thereby producing resistant force that prevents the heel portion of a midsole from being deformed laterally or transversely when a shoe comes in contact with the ground. Thus, transverse deformation of the heel portion of a shoe is prevented.
However, it depends on the kind of athletics or athletes whether athletes land on the ground more frequently from the medial portions or from the lateral portions of the heels at the onset of landing. For example, since tennis or basketball players move more often in the transverse direction and the medial portions of their heels tend to first contact with the ground, the heels lean outwardly and so-called supination often occurs. On the other hand, since runners or joggers tend to land on the ground from the lateral portions of their heels and the load moves toward the toes, the heels lean inwardly and so-called pronation often occurs.
Such pronation and supination are normal movements when a shoe comes in contact with the ground. But over-pronation or over-supination may cause injuries to the ankle, knee and hip of an athlete.
In the conventional midsole design, there is provided a corrugated sheet having a constant wave configuration in both the transverse direction and the longitudinal direction of the heel portion. Therefore, the prior art midsole has a constant compressive hardness (hardness to deform against the compressive force) throughout the whole midsole and as a result, it cannot control effectively pronation and supination of the foot of an athlete although controlling them is required according to the kind of athletics.
Generally, by inserting a corrugated sheet, the heel portion of a midsole tends to be less deformed in the transverse direction. When the corrugated sheet is formed especially from high elastic material the heel portion of a midsole tends to be less deformed in the vertical direction as well. Thus, by using a corrugated sheet, a portion where adequate cushioning properties is required on landing may show less cushioning properties.
On the other hand, good cushioning properties are indispensable requirements of athletic shoes, but too high cushioning properties may absorb an athletic power such as the running or jumping power of an athlete.
The object of the present invention is to provide a midsole assembly for an athletic shoe that can restrain over-pronation and over-supination on landing by preventing a shoe from being deformed in the transverse direction according to the kind of athletics and that can not only ensure adequate cushioning properties on landing but also prevent an athletic power from being lessened.